Centrifugal pipe casting apparatus



March 10, 1970 J. DENYSZYN 3,499,479

CENTRIFUGAL PIPE CASTING APPARATUS Filed May 18, 1967 CORE 88? SPOUT LONGITUDINAL MOVEMENT DURING CASTING CENTRIFUGAL LOCK SUPPORT CENTRIFUGAL LOCK COVER PLATE CENTRIFUGAL LOCK FINGER H64 INVENTOR JEAN DENYSZYN ATTORNEY United States Patent 3,499,479 CENTRIFUGAL PIPE CASTING APPARATUS Jean Denyszyn, Lynchburg, Va., assignor to Gla norgan Pipe & Foundry Co., a corporation of Virginia Filed May 18, 1967, Ser. No. 639,535 Int. Cl. B22d 13/02 US. Cl. 164-302 6 Claims ABSTRACT OF THE DISCLOSURE Centrifugal pipe casting utilizing a rotatable mold and a permanent-type reusable core for partially closing the mold at its pipe withdrawal end. The portion of the core facing casting material within the mold presents a surface with indentions for receiving and solidifying casting material so as to hold the end of the pipe and prevent distortion and end cracking prior to removal of the pipe from the mold.

This invention is concerned with centrifugal casting of pipe. In its more specific aspects, the invention is concerned with a permanent-type core which can be used repeatedly with centrifugal casting apparatus in the formation of no-hub pipe.

In the centrifugal casting of iron pipe, a controlled amount of molten iron is fed into a rotating elongated mold which moves longitudinally during casting to form a pipe. The rotating mold is a permanent or semi-permanent structure which must be open at one end for withdrawal of the cast pipe. During casting, that end of the rotating mold must be partially closed with a core to form the bell end of the pipe and retain metal in the mold for the entire casting. Sch cores must be readily removable upon completion of each cast.

To a large extent, the art has relied on use of expendable-type sand cores which are friable and can be removed from the mold and the pipe upon completion of each cast. Manufacture of such sand cores, the careful handling of cores required, removal of sand from the cast pipe, and other such problems increase the cost of manufacturing cast pipe using sand cores. It is also difficult to manufacture uniform, symmetrical sand cores which will con sistently fit the bell end of a rotating mold and provide crack and distortion-free pipe ends. In practice cracks are ordinarily formed in the pipe ends by metal which runs between the mold and the sand core. This metal forms fins on the pipe which, due to rapid cooling, generate cracks which are propagated into the pipe.

An object of the present invention is to provide casting apparatus able to withstand continuous rugged use and semi-automated functioning with a minimum of attention by working personnel. Also to provide casting apparatus which will consistently produce uniform product which does not need trimming, cleaning, or machining to be within required specifications. To meet these requirements a permanent-type, metallic core which can be accurately and quickly fitted to a rotatable mold is provided. Further, a metallic core is provided which is adaptable for use with self-locking mechanisms for rotatable molds.

However, it has been found that merely substituting metallic cores for sand cores does not provide the yield and economies required for commercial production. Many of the difiiculties encountered are believed to stem, at least in part, from too rapid chilling of molten metal contacting a metallic core. This rapid chilling of the metal at the bell end of the pipe is believed to be the cause of the distortion produced, for example an elliptical shape occurs at the bell end of the pipe rather than the desired circular configuration. Cracking of the pipe at the bell end as a result of this distortion or because of fin formation also decreases the yield. Distortion and end cracking caused by Patented Mar. 10, 1970 ice metallic cores have been found to decrease yield in excess of twenty percent so that ithas not been economically possible, prior to the present invention, to replace sand cores with permanent-type cores.

It is the primary objective of the present invention to provide a permanent-type core, which circumvents the above-described pipe casting problems, which uniformly produces crack-free and distortion-free pipe, and which can be used repeatedly, notwithstanding rough handling and extreme thermal stresses.

Referring to the accompanying drawings:

FIGURE 1 is a schematic view of centrifugal casting apparatus,

FIGURE 2 is a cross-sectional view of portion of a rotatable mold casting apparatus and a permanent-type core embodying the present invention,

FIGURE 3 is an end view of a portion of permanenttype core embodying the present invention, and

FIGURE 4 is a sectional view of a portion of the core of FIGURE 3.

In operation of the apparatus shown in FIGURE 1, molten metal is controllably fed for each casting operation from pouring box 12 to the interior of rotatable mold 14 through spout 16. At the beginning of the cast spout 16 extends about half the length of the mold toward its bell end. Rotatable mold 14 is spun about longitudinal axis 18 during each casting operation.

Prior to casting, core 20 is fitted to the rotatable mold 14. At the start of casting, metal from spout 16 contacts facing 22 of core 20. The metal is fed at such a rate, and the rotatable mold moves longitudinally (as indicated by arrow 26) at such a rate that a substantially uniform thickness pipe 24 is formed. Casting machines using a rotatable, longitudinally moving mold, e.g. Delavaud centrifugal pipe casting machines, are well known in the art and no further explanation of the general principle of operation is required for an understanding of the invention. The removable core problems discussed above are also well known in the art and have constrained these semi-automatic machines to use of sand cores for many years.

FIGURE 2 shows the permanent-type core of the present invention and portions of a rotatable mold along with self-locking structure. Core 28 is substantially symmetrical about longitudinal axis 30 and has an elongated hollow tubular configuration. The hollow portion of core 28 is in communication with the hollow tubular internal cavity of mold 34. The interior surface of core 28 is generally smooth and curvilinear defining a portion of a conical surface. The exterior surface of core body 32, which includes shoulder 33, has a configuration adapted for functioning of centrifugally operated self-locking fingers such as that shown at 36. Rotation of the mold provides the force for functioning of the self-locking mechanism. Other suitable locking mechanisms may be used in practice of the invention.

Core 28 is removably secured to rotatable pipe mold 34 and presents a patterned surface to a portion of the hollow tubular internal cavity defined by rotatable pipe mold 34. The patterned surface of one end of core 28 closes a portion of the hollow internal cavity of rotatable mold 34 contiguous to the internal periphery of the mold. The patterned surface presented by core 28 contacts molten metal poured into the mold.

Contact of molten metal with a metallic core is believed to have been responsible for the problems experienced before the present invention. Rapid chilling of the casting metal where contact was made with the core, and the differential chilling of metal contacting the core and metal contacting the mold, caused distortion of the pipe at the bell end. An elliptical configuration at the bell end of the cast pipe resulted rather than the desired circular configuration. Normally the ellipticalness extended several inches along the length of the pipe. As a result, either the entire pipe was scrapped or some portion of the pipe had to be cut off in order to salvage a pipe with limited uses, so that commercially acceptable yield could not be obtained.

The present invention solved these difiiculties by devising means for holding metal at the bell end of the pipe during the casting and pipe forming stages to prevent shrinkage, distortion, and cracking at the pipe end.

In practice, the core body configuration of the present invention can vary widely to suit the type of lock design employed. However, a core facing insert 40 is positioned at the end of core 28 contacting the rotatable mold 34. Diametral dimensions of core facing insert 40 are selected to maintain the pipe ends within thickness requirements. The facing insert 40 fits firmly into the mold to keep molten metal from between the core and the mold. That portion of core facing insert 40 which comes into direct contact with the molten metal is manufactured with recesses for receiving and solidifying casting metal so as to hold the bell end of the pipe against radial shrinkage forces during casting of the remainder of the pipe and until the pipe is removed from the mold.

Recesses in the core facing insert 40 can very in shape, depth and number depending on the type of metal being cast and the size pipe being cast. They can be formed in core facing insert 40' by various means including drilling and knurling.

In the embodiment shown in FIGURES 3 and 4 a plurality of indentations, such as 44, are used. These indentations can be distributed uniformly about core facing insert 46 in order to provide uniform gripping of the metal. Preferably the outer configuration of the indentations is curvilinear in order to avoid opportunity for forming minor cracks at the end surface of the pipe.

The depth of the indentations can vary depending on the diameter of the pipe being cast and the type of metal being cast. A depth of about & has been found satisfactory for standard cast iron pipe. The depth of the indentations should be sufficitent to hold the pipe against radial shrinkage forces. However, the depth of the indentations should not cause difficulty in removing the core or require removal of protrusions formed in the end surface of the pipe by the metal which is cast in the indentations.

The number of indentations can also vary with the size of the pipe. In a representative embodiment of the invention for casting four-inch diameter pipe, thirty indentations of Ms" outer diameter, depth, and a conical configuration as shown in FIGURE 4 have been found to be satisfactory. With a three-inch diameter pipe, twenty-four such indentations have been found to be satisfactory.

Considering useful life of a core, unexpected results are obtained by using brass for the core facing means. This longer life is believed to stem from the better thermal conductivity of the brass than that available with other suitable metals such as stainless steel. In practice a brass facing means about A in thickness, with recess means as above described, is welded to the core body. Suitable core body metal is ductile iron. This combination has resulted in long useful life, in excess of 5000 casts per core, notwithstanding the thermal shock encountered when the core is immersed in water after each casting.

Suitable metals for the core facing means include stainless steel, steel, iron, etc. Also satisfactory operation can be obtained by casting the entire core from a metal such as ductile iron and preparing the above described pattern in the face which contacts the molten metal. However, a brass core facing means and ductile iron core body combines features which make the core perform satisfactorily during each cast and rugged enough to withstand thousands of casts.

Alternate heating of the core during casting and cooling by quenching in water immediately after casting cause thermal fatigue which eventually determines the life of the core. This can be circumvented by eliminating the quenching step, but advantages, such as ease of handling of the core by the operator after quenching, make the quenching practice more suitable economically.

The present invention eliminates the problem of ellipticalness and end cracking in centrifugal pipe casting and provides permanent type apparatus able to withstand the rugged use and thermal stresses encountered. As a result, the yield and quality of the product, and production rate of centrifugal casting apparatus, are increased. Specific structure and materials have been set forth in disclosing the invention. However, the scope of the invention is not limited to such disclosure but rather is to be determined from the appended claims.

What is claimed is:

1. A reusable core for partially closing a rotatable mold at its inner periphery during centrifugal casting of pipe, the core comprising metallic core body means having a longitudinal axis, with the core being symmetrically disposed about the longitudinal axis, and

metallic core facing means secured to one end of the core body means and adapted to close a portion of the rotatable mold contiguous to the inner periphery of the rotatable mold at its pipe withdrawal end,

the core facing means having a configuration defining a substantially planar surface and portions recessed below and bounded completely about their periphery by the substantially planar surface for receiving and solidifying casting material so as to hold a pipe during casting at the pipe withdrawal end of the rotatable mold.

2. The structure of claim 1 in which the core body means comprises ductile iron and the core facing means comprises brass.

3. A reusable core for partially closing an elongated rotatable mold at its pipe withdrawal end during centrifugal casting of pipe, the rotatable mold being of circular cross-section in a plane perpendicular to its longitudinal axis and defining an internal cavity having an inner periphery, the reusable core comprising core body means having a longitudinal axis, with the core body means being adapted to be positioned with its longitudinal axis substantially co-extensive with the longitudinal axis of the rotatable mold, the core body means being made of metal which is substantially symmetrically disposed about the longitudinal axis of the core and having an external configuration defining shoulder means for removably locking the core to the rotatable mold, and

metallic core facing means secured to one longitudinal end of the core body means and adapted to partially close a portion of the internal cavity of the rotatable mold during casting of a pipe, with the partially closed portion extending radially inwardly from the inner periphery of the internal cavity of the rotatable mold,

the metallic core facing means defining a pattern of indentations spaced from inner and outer peripheries of the facing means for receiving and solidifying casting material so as to hold the pipe at the pipe withdrawal end of the rotatable mold during casting and solidification of the remainder of the pipe.

4. In combination with centrifugal pipe casting apparatus having an elongated hollow rotatable mold having a longitudinal axis and being of substantially circular configuration in a cross-sectional plane perpendicular to its longitudinal axis,

a self-locking reusable-type metallic core having a longitudinal axis and a hollow tubular configuration symmetrically disposed about its longitudinal axis,

the core being removably secured to the longitudinal end of the rotatable mold through which a cast pipe is removed with the longitudinal axis of the core being substantially co-extensive with the longitudinal axis of the rotatable mold so as to close a portion of the pipe withdrawal end of the hollow rotatable mold contiguous to the inner periphery and prevent escape of molten casting material between the mold and the core, the core presenting at its longitudinal and partially closing the rotatable mold a metallic surface for contacting material being cast, the metallic surface having an inner and outer diameter and a patterned configuration defining recess means spaced from the inner and outer diameter of the metallic surface for receiving and solidifying material being cast so as to hold a pipe at the pipe withdrawal end of the rotatable mold and prevent radial shrinkage during casting and solidification of the remainder of the pipe. 5. A reusable, permanent-type, metallic core for use with centrifugal pipe casting apparatus utilizing a rotatable mold defining an elongated hollow tubular cavity having an internal surface for molding casting material and a pipe withdrawal end,

the metallic core being adapted to be removably secured to the rotatable mold so as to partially close a portion of the pipe withdrawal end of the elongated hollow tubular cavity spaced from its longitudinal axis by presenting a patterned surface having an outer periphery contiguous to the internal surface of the rotatable mold and an inner periphery spaced inwardly therefrom toward the longitudinal axis of elongated hollow tubular cavity,

the patterned surface of the metallic core defining recess means for receiving and solidifying casting material so as to hold a pipe at the pipe withdrawal end of the pipe rotatable mold,

the recess means being spaced about the patterned surface intermediate its inner and outer peripheries.

6. The structure of claim 5 in which the recess means defined by the patterned surface of the metallic core includes a plurality of curvilinear configuration indentations uniformly distributed about the patterned surface of the metallic core.

References Cited UNITED STATES PATENTS 8/1965 Haughton et a1. l64299 6/1967 Latour 164286 

